The present invention relates to a magnetic recording/reproducing apparatus such as a home video tape recorder or the like and, more particularly, to an autotracking control apparatus of a magnetic recording/reproducing apparatus which is suitable for the case where magnetic rotary heads automatically scan the record tracks obliquely formed on a magnetic tape by way of the helical scan system.
Recently, in addition to conventional home video tape recorders (hereinafter, abbreviated as VTR), what are called Hi-Fi video tape recorders (hereinafter, abbreviated as Hi-Fi VTR) which can record and reproduce audio signals with a high degree of fidelity have been commercialized.
Such Hi-Fi VTR intends to improve a sound quality due to an increase in relative speed between the tape and the head in a manner that the audio information, which has been hitherto recorded and reproduced by the fixed head, is frequency modulated and then recorded on the magnetic tape by use of a pair of rotary heads on the drum.
Such Hi-Fi VTR that attaches importance to the sound quality is equipped with a pair of rotary heads and also a conventional fixed head for recording and reproducing audio information and is used for various purposes such as in the following cases. Namely, there are the cases (i) where only audio signals are recorded by the audio rotary heads without recording a video signal; (ii) where the magnetic tape on which audio signals have been recorded by a conventional VTR, namely, audio signals have been recorded by the fixed head is reproduced; (iii) where both audio and video signals are recorded and reproduced by the rotary heads; (iv) where a video signal is recorded by the rotary heads and audio signals are recorded by only the fixed head; and (v) where a video signal is recorded by the rotary heads and audio signals are recorded by both the rotary and fixed heads.
Although Hi-Fi VTR is used in the foregoing various cases, the Hi-Fi VTR in which the auto-tracking is performed does not exist at present so far as the inventors of the present application know. In execution of the auto-tracking in Hi-Fi VTR, various kinds of problems are produced because of a reason such that the Hi-Fi VTR can be used in the various manner. An explanation will then be made hereinbelow with respect to an example of conventional auto-tracking apparatuses and problems which would be caused when such conventional auto-tracking apparatus is to be used for the Hi-Fi VTR.
FIG. 1 is a block diagram showing an example of an auto-tracking circuit which is used in a conventional magnetic recording/reproducing apparatus which records and reproduces audio signals using the fixed head. FIG. 2 is a diagram showing the waveforms in various points in the circuit of FIG. 1. FIG. 3 is a supplementary explanatory diagram.
An example of an auto-tracking apparatus similar to the conventional auto-tracking apparatus shown in FIG. 1 is disclosed in Japanese Patent Unexamined Publication No. 54-41114.
Reference may be made to the U.S. patent application Ser. No. 754,908 filed on July 15, 1985 (corresponding European patent application Ser. No. 85108880.7 filed on July 16, 1985), based on Japanese patent application No. 59-146759 filed July 17, 1984.
In FIG. 1, reference numeral 1 denotes a magnetic tape; 2 is a control pulse head (hereinafter, abbreviated as a CTLP head); 3 and 7 amplifiers for amplifying a control signal and a reproduced video signal, respectively; 4 and 11 delay circuits; 5 a window counter; 6 and 13 clock pulse generators; 8 an integrator; 9 and 10 waveform shaping circuits; 12 a monostable multivibrator; 14 a logic circuit; 15 a sampling counter; 16 a flip-flop; 17 an up/down counter; 18 a coincidence circuit; 19 a crystal resonator; 20 a crystal oscillator; 21 a frequency divider; 22 a ramp signal generator; 23 a phase comparator; 24 a capstan motor driving amplifier; 25 a capstan motor; 26 a speed control signal input terminal for switching among the standard reproducing mode, the one-third speed reproducing mode, and the like; 27 a reproduced video signal input terminal; 28 and 29 input terminals for receiving rotational phase detection signal of a pair of video rotary heads; and 30 a counter. In FIGS. 1 and 2, reference numerals 40 to 54 all represent voltage signals. In FIG. 3, numeral 70 denotes a magnetic tape; 71 and 72 are video heads; 73 and 74 track patterns recorded on the tape 70; 75 a drum motor; 76 a capstan motor; 77 and 78 trace loci of the centers of the video heads 71 and 72; 79 a reference signal generator; 80 and 81 phase control circuits; 82 a delay circuit; 83 a drum rotation detecting signal; and 84 a reproduced control pulse (hereinafter, abbreviated as a CTLP signal).
First, it is assumed that the track patterns 73 and 74 were recorded and formed on the magnetic tape 70 by the video heads 71 and 72, respectively. In this case, it is a general way to remove the adjacent disturbance by making the magnetizing directions of the heads differ with regard to both of the adjacent tracks 73 and 74 (practically speaking, the heads 71 and 72 are obliquely arranged at the angles +.theta..degree. and -.theta..degree. (azimuth angles) with respect to the longitudinal directions of the tracks, respectively). Therefore, assuming that the tracks 73 and 74 were respectively recorded by the video heads 71 and 72, in the case where one of the tracks is traced by the head the azimuth angle of which is the same as that of the head used when recording the same track, the output of the head becomes maximum, and in the opposite case, namely, in the case where one of the tracks is traced by the head which has the different azimuth angle from that used when recording, the output of the head becomes minimum. In the intermediate by the head having the same azimuth angle as that of the head used to record that track, the head output increases substantially in proportion to the area of the portion of the track which is scanned or traced by this head. Thus, for example, when the trace locus of the center of the head 71 is indicated at 77, the head output becomes maximum and in the case of the trace locus 78, the head output decreases than that maximum head output.
The drum motor 75 and capstan motor 76 are phase-controlled so that the rotary video heads 71 and 72 and the magnetic tape 70 in the magnetic recording/reproducing apparatus synchronously operate at a predetermined phase difference. Practically speaking, those synchronous operations are realized in a manner that the phase of the drum to which a pair of heads 71 and 72 are attached is locked by the phase control circuit 80 so that the phase of a reference signal 200 from the reference signal (30 Hz) generator 79 and the phase of the rotational phase detecting signal 83 of the drum motor 75 for driving the drum are locked, and at the same time a phase control is performed by the phase control circuit 81 so that the phase of the reproduced CTLP signal 84 and the phase of the reference signal 201 having a predetermined phase difference .phi. with regard to the reference signal 200 are locked. In this manner, the phase differences between the heads 71, 72 and the reproduced CTLP signal 84 are always fixed to constant value .phi.. Thus the rotary video heads 71 and 72 trace the track patterns 73 and 74 recorded. However, actually, since the video heads 71 and 72 are distantly positioned from the playback head for reproducing the CTLP signal 84, in the case where the tape recorded by a magnetic recording/reproducing apparatus is reproduced by another magnetic recording/reproducing apparatus, the locus, e.g., the locus indicated at 78 in FIG. 3 which is deviated from the trace locus (77 in FIG. 3) having the proper phase difference .phi. is traced due to expansion and contraction of the magnetic tape, variation of the positions where the heads are attached, or the like, so that the reproduced picture quality deteriorates. To prevent this deterioration, the delay circuit 82 is provided for a reference signal 201 (or reproduced CTLP signal 84) as shown in FIG. 3 and thereby making it possible to control the delay amount by the user. Such coordination among that heads and the tracks is a so-called "tracking". FIG. 1 is a block diagram showing one of conventional examples of such systems that automatically perform this tracking operation. In this example, the system in which the phase control is executed by delaying the phase of the reproduced CTLP signal is adopted.
The operation of the system of FIG. 1 will be explained hereinbelow. First, the rotational phase detecting signals of the drum inputted through the terminals 28 and 29 in FIG. 1 are waveform-shaped by the waveform shaping circuits 9 and 10 (40 and 41 in FIG. 2). Both of those signals 40 and 41 are the pulses which are generated for every rotation of 180.degree. of the drum 75 in FIG. 3. When the apparatus is constituted in a manner that both of those signals are generated at the timings which are almost simultaneous with the change-over timing of the heads 71 and 72, the information of the central portion of the screen of the television are traced by the heads 71 and 72 at the timings which are delayed by about 8 msec from both of those signals. (This is because the drum is rotating at a frequency of 30 Hz and the time required for one head to trace one track is a little over 16 msec.) Therefore, both of those signals are delayed by the delay circuit 11. Reference numeral 42 in FIG. 2 denotes the pulse which becomes a high level for this delay time. The tracking state can be most preferably monitored by sampling the reproduced signal outputs of the heads at the timing of the trailing edge of the pulse 42. Namely, the time of the trailing edge of the pulse 42 just corresponds to the central portion of a track formed obliquely on the magnetic tape relative to the longitudinal direction of the tape. The above-mentioned delay amount of 8 msec is set on the basis of the principle that when the reproduced signal output of the head is sampled at the timing corresponding to that central portion, the reproduced output signal can be almost certainly sampled even if the expansion and contraction of the magnetic tape, compatibility with other magnetic recording/reproducing apparatuses, and other various factors are considered.
The amplitude of the reproduced signal derived by the foregoing sampling is converted to the digital values in the following manner. The converting operation in this case will be first explained hereinbelow. First, the reproduced video signal (the signal 43 in FIG. 2) inputted through the terminal 27 is amplified by the amplifier 7 and smoothed by the integrator 8 (the signal 44 in FIG. 2). The monostable multivibrator 12 generates a signal which becomes a high level for the period of time proportional to the potential of the signal 44. For instance, such a monostable multivibrator can be easily realized in the following manner. A comparator having two inputs is used and the output (i.e., the signal 44) of the integrator 8 is connected to one input. The other input is connected so as to receive the voltage across a capacitor which increases at a constant rate as it receives the supply of a constant current from a constant current source which is triggered in response to the trailing edge of the output signal 42 of the delay circuit 11 and starts the supply of the constant current. The timing when the voltage of the capacitor has reached the potential of the signal 44 is detected by the comparator and the charges of the capacitor are discharged, then the comparator waits until a trigger signal is newly inputted, or the like. The comparator is constituted such that an output of the comparator becomes high for the charge period of time of the capacitor. Numeral 45 in FIG. 2 indicates an output signal of the monostable multivibrator 12. Further, the clock pulse generator 13 generates a clock pulse for only the period of time when the signal 45 is high and its output signal is indicated at 46. This clock pulse 46 is supplied to the logic circuit 14. The logic circuit 14 determines the increase or decrease of the delay amount of the running phase of the magnetic tape for the time period when the output signal 47 of the sampling counter 15 is high. The signal 47 is generated one pulse for every N-period of the rotation detecting signal 42 of the rotary heads. In the case of FIG. 2, N is set to 3. Namely, the value of N determines the period for the above-mentioned decision. The logic circuit 14 has therein a counter for accumulating and counting the clock pulse 46 for the time period commensurate with the latest N periods of the signal 42, a holder for holding the count value for the previous N periods immediately before those latest N periods, and a comparator. The accumulated count value B of the clock pulse 46 for the latest N periods which was accumulated and counted by that counter is compared with the count value A for the previous N periods held in the holder. When A&gt;B (old data is larger than the latest data) as the result of this comparison, the pulse 48 is outputted. When A.ltoreq.B (the old data is smaller than or equal to the latest data), no pulse is outputted. Triggered by the signal 48, the flip-flop 16 changes the level of its output 49. The up/down counter 17 discriminates the signal 49 as the count polarity (high: up-count, low: down-count) and after the level of the polarity signal 49 was established in dependence on the presence or absence of the pulse 48, the counter 17, depending upon the count porality, up- or down-counts in response to the trailing edge of the signal 47. In the example of FIG. 2, therefore, assuming that the initial value of the up/down counter 17 is M, the count value is counted up when the signal 49 is high. When the signal 49 becomes low after the count value became M+1, the count value is counted down and changes to M.
In addition to the above-mentioned operation, the delay loop of the CTLP signal exists. In this delay loop, after the reproduced CTLP signal 50 was amplified by the amplifier 3, it is slightly delayed by the delay circuit 4 and the window counter 5 is made operative in response to the trailing edge of the output signal 51 of the delay circuit 4. The clock pulse generator 6 generates the clock pulse train 53 in response to the output 52 of the counter 5. The coincidence circuit 18 outputs the delayed CTLP signal 54 when the number of clock pulses of the clock pulse train 53 coincides with the value held in the up/down counter 17. In this example, therefore, as shown at 54 in FIG. 2, the CTLP output signal which contains pulses delayed by T.sub.d from the CTLP signal 50 is generated at the timing when the number of pulses of the clock pulse train 53 coincides with M, M+1 and M. The phase of the CTLP signal 54 changes with a resolution corresponding to one period of the clock pulse 53.
The foregoing overall control can be summarized as follows. That is, the delay amount of the CTLP signal to be phase-controlled is controlled so that the output from the head becomes maximum. This is because, this delay amount is held in the up/down counter and this count value is controlled so that the output from the head increases. In other words, in the case where the output level of the video head after the change of the delay amount is larger than the previous value, namely, than the head output level before the delay amount is changed, the delay amount of the CTLP signal is continued to be changed in the same direction. In other words, the CTLP signal is further increased or further decreased depending upon the previous change direction. In the opposite case, the change direction is reversed. In this manner, the delay amount is varied so that the head output data always increases.
The signal of, e.g., 3.58 MHz generated from the oscillator 20 is divided by the frequency divider 21 and changed to the signal of a low frequency of, e.g., 30 Hz. The ramp signal generator 22 is triggered by this low-frequency signal and generates a repetitive wave of a constant peak value of a triangular wave. The phase comparator 23 compares an output of the ramp signal generator 22 with the CTLP signal 54 of the coincidence circuit 18 and samples and holds the peak value of the ramp signal at the generation timing of the CTLP signal 54. In this way, the delay amount of the CTLP signal 54 is converted to the signal having the level corresponding to the delay amount by the phase comparator 23. The motor driving amplifier 24 amplifies an output signal of the phase comparator 23. The capstan motor 25 is controlled at the speed corresponding to the delay amount of the CTLP signal 54 due to an output of the amplifier 24.
As described earlier, in Hi-Fi VTR, the audio information which, conventionally, is recorded and reproduced by the fixed head is frequency modulated by a pair of rotary heads attached to the drum and then recorded on the magnetic tape. In addition, such Hi-Fi VTR is also equipped with the fixed head similar to the conventional one so that the magnetic tape on which the audio information has been recorded by the fixed head can be also reproduced.
In the case where the conventional auto-tracking system as mentioned above is to be applied to such Hi-Fi VTR, there would be the following drawbacks. Namely, in such Hi-Fi VTR that attaches importance to the sound quality, only the audio signals are recorded by the audio rotary heads in many cases. In this case, the auto-tracking based on the output from the video head cannot be performed. On the contrary, in the case of the normal recorded tape on which audio signals were recorded by the fixed head of the conventional apparatus, the auto-tracking cannot be performed by use of the outputs of the audio rotary heads. In addition, it is important that the good tracking can be derived by executing the auto-tracking by using the audio signals in the case where both of the video and audio signals were recorded. This is because the width of the video head is generally wider than the widths of the audio heads and there is an allowance for a slight tracking deviation in the case of the video head; on the contrary, the audio heads are narrow and sensitive for the tracking deviation. For those reasons, it is necessary to smoothly and accurately perform the auto-tracking even for the tapes recorded by any recording system by making use of the outputs of the audio and video rotary heads.